package org.openmuc.jsml.tl;

/*
 * Copyright Fraunhofer ISE, 2010
 * Author(s): Michael Zillgith
 *    
 * This file is part of jSML.
 * For more information visit http://www.openmuc.org
 * 
 * jSML is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * jSML is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with jSML.  If not, see <http://www.gnu.org/licenses/>.
 * 
 */

import java.io.DataInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * 
 * Implements SML transport layer version 1
 * 
 * Extracts the next SML File from a DataInputStream
 * 
 * @author mzillgit
 * 
 */
public class SMLMessageExtractor {

	/*
	 * table to calculate crc16
	 */
	private static final int[] table = { 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48,
			0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c,
			0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210,
			0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
			0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef,
			0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 0xce4c, 0xdfc5,
			0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3,
			0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f, 0x4014, 0x519d,
			0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387,
			0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862,
			0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52,
			0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff, 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
			0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e,
			0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402,
			0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5,
			0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df,
			0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5,
			0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3,
			0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d,
			0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 };

	private DataInputStream inputStream;

	private ByteBuffer smlMessageBuffer = ByteBuffer.allocate(2000);

	private byte[] smlMessage = null;

	private int crc = 0xffff;

	private byte[] buffer = new byte[8];

	private int bufferEnd = 0;

	private long timeoutInMillies;

	private boolean startSequenceFound = false;

	public SMLMessageExtractor(DataInputStream inputStream, long timeoutInMillies) throws IOException {
		this.inputStream = inputStream;
		this.timeoutInMillies = timeoutInMillies;
		smlMessageBuffer.rewind();
	}

	public byte[] getSmlMessage() throws IOException {
		waitForStartSequence();
		waitForStopSequence();
		return smlMessage;
	}

	private void waitForStartSequence() throws IOException {
		while (!startSequenceFound) {

			fillBufferWithTimeout();

			if (checkForStartSequence()) {
				crc = 0xffff; /* reset CRC */

				clearBuffer();

				startSequenceFound = true;
				return;
			}

			dropByte();
		}
	}

	private void waitForStopSequence() throws IOException {
		boolean stopSequenceFound = false;

		while (!stopSequenceFound) {
			fillBufferWithTimeout();

			if (checkForEscapeSequence()) {
				if (checkForEscapedEscapeSequence()) {
					for (int i = 4; i < 8; i++) {
						incrementalCRC(buffer[i]);
					}

					bufferEnd = 4;
					clearBuffer();
				}
				else { /* end sequence */
					stopSequenceFound = true;
					int numStuffBytes = buffer[5];

					for (int i = 0; i < 6; i++) {
						incrementalCRC(buffer[i]);
					}

					int receivedCRC = (0xff & (buffer[6])) * 0x100 + (0xff & buffer[7]);

					if ((buffer[4] != 0x1a) || (numStuffBytes > 3)) {
						throw new IOException("Termination sequence is wrong");
					}

					crc ^= 0xffff;
					crc = ((crc & 0xff) << 8) | ((crc & 0xff00) >> 8);

					if (receivedCRC != crc) {
						throw new IOException("wrong crc");
					}

					int bufferLength = smlMessageBuffer.position();

					smlMessage = new byte[bufferLength - numStuffBytes];
					smlMessageBuffer.rewind();
					smlMessageBuffer.get(smlMessage);
				}
			}
			else {
				incrementalCRC(dropByte());
			}
		}
	}

	private void clearBuffer() {
		while (bufferEnd > 0) {
			incrementalCRC(dropByte());
		}
	}

	private byte dropByte() {
		byte droppedByte = buffer[0];

		for (int i = 0; i < (bufferEnd - 1); i++) {
			buffer[i] = buffer[i + 1];
		}

		bufferEnd--;

		if (startSequenceFound) {
			smlMessageBuffer.put(droppedByte);
		}

		return droppedByte;
	}

	private void incrementalCRC(byte msgByte) {
		crc = (crc >> 8) ^ table[(crc ^ msgByte) & 0xff];
	}

	private void fillBufferWithTimeout() throws IOException {
		long lastRead = System.currentTimeMillis();

		while (bufferEnd < 8) {

			if ((System.currentTimeMillis() - lastRead) > timeoutInMillies) {
				throw new IOException("Timeout");
			}

			if (inputStream.available() > 0) {
				buffer[bufferEnd] = inputStream.readByte();
				bufferEnd++;
				lastRead = System.currentTimeMillis();
			}
			else {
				try {
					Thread.sleep(50);
				} catch (InterruptedException e) {
				}
			}
		}
	}

	private boolean checkForEscapeSequence() {
		for (int i = 0; i < 4; i++) {
			if (buffer[i] != 0x1b) {
				return false;
			}
		}

		return true;
	}

	private boolean checkForEscapedEscapeSequence() {
		for (int i = 4; i < 8; i++) {
			if (buffer[i] != 0x1b) {
				return false;
			}
		}
		return true;
	}

	private boolean checkForStartSequence() {
		if (checkForEscapeSequence() == false) {
			return false;
		}

		for (int i = 4; i < 8; i++) {
			if (buffer[i] != 0x01) {
				return false;
			}
		}

		return true;
	}

}